Isolated mild ventriculomegaly (IMVM) is one of the most frequent diagnoses made on routine prenatal ultrasound. Despite its relatively common occurrence, the neurodevelopmental outcome of fetuses diagnosed with IMVM on prenatal ultrasound cannot be accurately determined. Indeed, studies to date indicate that anywhere from 0% to 36% of fetuses will develop neurodevelopmental disabilities during infancy or childhood, making prenatal counseling extremely challenging and frustrating for clinicians. Recent technical advances in fetal magnetic resonance (MR) imaging have resulted in improved visualization of the fetal brain compared with prenatal ultrasound. As such, fetal MR imaging offers the ability to more closely and non-invasively study both macrostructural and microstructural changes during in utero brain development. The health relatedness of this proposal is to improve prenatal counseling through advances in fetal MR imaging and to prenatally identify those fetuses at higher risk for neurodevelopmental disabilities so that patients can benefit from earlier postnatal treatment interventions. The central hypotheses of this proposal are that fetuses with IMVM have abnormalities in brain development, the abnormalities can be assessed by fetal MR imaging, and that these abnormalities correlate with neurodevelopmental outcome. The Specific Aims are 1) to characterize microstructural changes in the developing white matter of fetuses with IMVM, 2) to identify macrostructural abnormalities in fetuses with IMVM, and 3) to correlate MR imaging markers from Specific Aims 1 and 2 with neurodevelopmental outcome at 12 and 30 months of age. The broad, long-term objectives are to better understand the etiology and pathogenesis of IMVM; to identify imaging parameters that can be used to better predict neurodevelopmental outcome; and to translate this knowledge into improved prenatal counseling, early treatment intervention during infancy, and future studies on the prevention and treatment of IMVM.